Which vessel is categorized as a sailing vessel?

A sailing vessel is specifically defined as one that primarily uses sails for propulsion, relying on wind power rather than mechanical engines. When considering the characteristics provided, a vessel that operates solely under sail without any engine confirms to this definition, making it a true sailing vessel. This vessel harnesses wind energy to navigate, which aligns with the fundamental principles of sailing.

In contrast, a motorboat that uses wind power, while it might be capable of sailing, typically incorporates an engine and therefore does not fit the strict classification of a sailing vessel. Similarly, a fishing vessel equipped with an engine primarily depends on that engine for movement, and a vessel used only for rowing does not involve sails at all. Thus, the correct answer is a vessel under sail without an engine in use since it is the only option that embodies the true essence of a sailing vessel.